Work Vehicle

ABSTRACT

This work vehicle is provided with an emergency brake function for quickly bringing said work vehicle to an emergency stop when an abnormality has occurred inside of the vehicle. The work vehicle comprises: a foot brake for braking left and right rear wheels; an autonomous travel unit that enables autonomous travel of the vehicle; and an electric actuator for switching the foot brake between a braking state and a release state. The autonomous travel unit comprises a control unit that controls the operation of the electric actuator. When in an autonomous travel mode, the control unit controls the operation of the electric actuator and switches the foot brake from the release state to the braking state when an abnormality is detected inside of the vehicle on the basis of detection information from a vehicle state detection device for detecting the state of each part of the vehicle, or when an emergency stop command is acquired from a wireless communication device set so as to be capable of wireless communication with the autonomous travel unit.

TECHNICAL FIELD

The present invention relates to a work vehicle including aboarding-type driver unit and a foot brake for braking a driving device.

BACKGROUND ART

Some passenger cars use a driving support device and a driving supportmethod in which emergency brake control is performed when there is arisk of collision with a preceding vehicle (for example, refer to PTL1).

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Publication No. 2017-43193

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

In recent years, work vehicles, such as tractors, have been automated toenable autonomous driving of work vehicles through the use of satellitepositioning systems (navigation satellite system (NSS)), such as aglobal positioning system (GPS). Advancement in such automation of workvehicles leads to the realization of unmanned work vehicles that arecapable of autonomous driving of the unmanned work vehicles. In order torealize such an unmanned work vehicle that is capable of autonomousdriving, the work vehicle needs to have an emergency brake function forquickly stopping the work vehicle when an error occurs in the controlsystem related to autonomous driving, such as a speed change controlsystem and a steering control system.

Therefore, it is conceivable that the emergency brake function adoptedin passenger cars be applied to the work vehicles. However, theemergency brake function adopted in passenger cars is a driving supportdevice or a driving support method such as those described in PTL 1,which are intended for the prevention of collision with a precedingvehicle and the reduction of collision damage. For this reason, it isnecessary to develop a unique emergency brake function in order to solvethe above problems.

Since a work vehicle capable of unmanned autonomous driving isoriginally configured to be driven by a passenger, the emergency brakefunction must not hinder the manual driving by the passenger.

In view of such a situation, a main object of the present invention isto provide an emergency brake function capable of quickly stopping awork vehicle when an error occurs inside the vehicle.

Means for Solving the Problems

A first characteristic configuration of the present invention is in awork vehicle including:

a boarding-type driver unit;

a foot brake that brakes a driving device;

an autonomous drive unit that enables autonomous drive of a vehicle; and

an electric actuator that switches the foot brake between a brakingstate for braking the driving device and a released state for releasingthe braking, wherein,

the driver unit includes a mode selector that enables selection of anautonomous drive mode in which the autonomous drive unit autonomouslydrives the vehicle,

the autonomous drive unit includes a control unit that controls anoperation of the electric actuator, and

in the autonomous drive mode, if an error is detected inside the vehiclebased on detection information from a vehicle state detection devicethat detects a state of each component in the vehicle, or if anemergency stop command is obtained from a wireless communication devicethat is capable of wireless communication with the autonomous driveunit, the control unit controls the operation of the electric actuatorand switches the foot brake from the released state to the brakingstate.

According to this configuration, if an error occurs inside the vehicle,the electric actuator switches the foot brake to the braking state underthe control of the control unit when the control unit detects an errorinside the vehicle on the basis of detection information from thevehicle state detection device or when the control unit obtains anemergency stop command sent by an outside administrator through thewireless communication device in response to noticing an error. As aresult, the work vehicle can be quickly braked and stopped.

In this way, even if an error occurs inside the vehicle in an unmanneddrive state in which the tractor autonomously drives without apassenger, the work vehicle can be quickly braked and stopped.

Since the foot brake is highly reliable and does not cause problems evenwhen it is frequently used during manual driving by the passenger, it ispossible to certainly stop brake and stop the work vehicle in anunmanned state.

By using the foot brake for an emergency stop, it is possible to avoidthe complication of the structure due to introduction of a new brakededicated to the emergency stop.

In a second characteristic configuration,

the driver unit includes an operating tool for brake release, and

if the operation tool is manually operated in the braking state of thefoot brake by the operation of the electric actuator, the control unitcontrols the operation of the electric actuator and switches the footbrake from the braking state to the released state.

According to this configuration, in an emergency stop state in which theelectric actuator switches the foot brake to the braking state under thecontrol of the control unit, the administrator or the like can get intothe driver unit and operate the operation tool to release the emergencystop state of the work vehicle at any time.

This enables the administrator who has gotten into the driver unit tomanually drive the work vehicle, and the work vehicle can be moved to asafe place or a repair shop by manual driving.

In a third characteristic configuration,

if the autonomous drive mode is deselected when the foot brake is to beswitched to the braking state and if the autonomous drive mode isselected by the mode selector after the deselection, the control unitdetermines whether or not an error has occurred inside the vehicle onthe basis of detection information from the vehicle state detectiondevice and permits a transition to the autonomous drive mode when it isdetermined that no errors have occurred inside the vehicle.

According to this configuration, in an emergency stop state of the workvehicle under the control of the control unit, even when the emergencystop under the control of the control unit is released, the work vehiclewill not be able to autonomously drive until the control unit determinesthat there is no error inside the vehicle.

This makes it possible to prevent the automatic driving of the workvehicle while an error continues inside the vehicle.

A fourth characteristic configuration includes:

an electronically controlled engine,

wherein, if the control unit controls the operation of the electricactuator and the foot brake is switched from the released state to thebraking state, the control unit automatically stops the engine.

According to this configuration, in the case where the work vehicleincludes a work device driven by power from an engine, the work vehiclecan be urgently stopped and the work device can be stopped under thecontrol of the control unit.

In this way, the emergency stop of the work vehicle can be morepreferably performed along with the stop of the work device.

In a fifth characteristic configuration,

if the operation of the electric actuator switches the foot brake to thebraking state, and if power is turned on again by turning on a keyswitch provided in the driver unit after the power has been turned offby turning off the key switch in a state in which the engine isautomatically stopped, the control unit permits activation of the engineand switches the foot brake form the braking state to the released stateby controlling the operation of the actuator.

According to this configuration, in an emergency stop state of the workvehicle under the control of the control unit, the emergency stop stateof the work vehicle can be released and the engine can be activatedsimply by the administrator or the like getting into the driver unit andoperating the key switch.

As a result, the work vehicle can be more readily switched to a state inwhich it can be manually driven, and the work vehicle can be moved to asafe place or a repair shop more quickly.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the schematic configuration of anautonomous drive system.

FIG. 2 is a block diagram illustrating the schematic configuration of anautonomous drive system.

FIG. 3 is a block diagram illustrating the schematic configurationrelated to a safety brake function.

FIG. 4 is a perspective view from the upper left rear side of a mainportion illustrating the configuration of a brake system.

FIG. 5 is a perspective view from the upper right rear side of a mainportion illustrating the configuration of a brake system.

FIG. 6 is a perspective view of a main portion of a brake systemillustrating the configuration of brake pedals and the vicinity.

FIG. 7 is a rear view of a main portion of a brake system illustratingthe configuration of brake pedals and the vicinity.

FIG. 8 is a perspective view from the upper right front side of a mainportion of a brake system illustrating the brake operation structure byan electric motor.

FIG. 9 is a perspective view from the upper right rear side of a mainportion of a brake system illustrating the brake operation structure byan electric motor.

FIG. 10 is a right side view of a main portion of a brake systemillustrating the brake operation structure by an electric motor.

FIG. 11 is a longitudinal left side cross-sectional view of a mainportion of a brake system illustrating foot brakes in a state notoperated by an electric motor.

FIG. 12 is a longitudinal left side cross-sectional view of a mainportion of a brake system illustrating foot brakes in a state operatedby an electric motor.

FIG. 13 is a graph illustrating the relation between the operationamount by the operation of an electric motor, a braking force, and anoperating load.

FIG. 14 is a flowchart of emergency stop control.

FIG. 15 is a diagram illustrating a home screen on a liquid crystalmonitor.

FIG. 16 is a diagram illustrating a safety-brake-check selection screenon a liquid crystal monitor.

FIG. 17 is a diagram illustrating a safety brake check screen on aliquid crystal monitor in which an initial check button is displayed inan inoperable state.

FIG. 18 is a diagram illustrating a safety brake check screen on aliquid crystal monitor in which an initial check button is displayed inan operable state.

FIG. 19 is a diagram illustrating a safety brake check screen on aliquid crystal monitor indicating that a check is being performed.

FIG. 20 is a diagram illustrating a safety brake check screen on aliquid crystal monitor indicating that a check has failed.

FIG. 21 is a diagram illustrating a safety brake check screen on aliquid crystal monitor indicating that a check has been completed.

FIG. 22 is a diagram illustrating an autonomous drive start screen on aliquid crystal monitor.

FIG. 23 is a diagram illustrating the sequence of an initial check(operation confirmation process).

FIG. 24 is a state transition diagram illustrating state transition inan initial check of a safety brake function unit.

FIG. 25 is a state transition diagram illustrating state transition inan error detection state of a safety brake function unit.

DESCRIPTION OF EMBODIMENTS

An embodiment in which a work vehicle according to the present inventionis applied to a tractor will now be described as an example of anembodiment of the present invention, with reference to the drawings.

Note that, besides a tractor, the work vehicle according to the presentinvention may be applied to a passenger work vehicle, such as a ridingmower, a riding rice transplanter, a combine, a carrier, a wheel loader,or a snowplow.

As illustrated in FIGS. 1 and 2, a tractor 1 exemplified by the presentembodiment is capable of autonomous driving by an autonomous drivesystem for work vehicles in a field or the like, which is an example ofa work area. The autonomous drive system includes an autonomous driveunit 2 and a mobile communication terminal 3. The autonomous drive unit2 is installed in the tractor 1. The mobile communication terminal 3 isan example of a wireless communication device set up to wirelesslycommunicate with the autonomous drive unit 2. The mobile communicationterminal 3 may be a tablet-type personal computer or a smart phoneincluding a multi-touch type display unit (for example, a liquid crystalpanel) 4 for displaying information regarding autonomous drive.

As illustrated in FIG. 1, a rear portion of the tractor 1 is coupled toa rotary tiller 6 via a three-point link mechanism 5 such that therotary tiller 6 can be raised, lowered, and rolled. The rotary tiller 6is an example of a work device. In this way, the tractor 1 is configuredfor rotary tilling specifications.

Note that, in place of the rotary tiller 6, the rear portion of thetractor 1 may be coupled to various work devices, such as a plow, a discharrow, a cultivator, a subsoiler, a seed planter, a spraying device,and a grass cutter.

As illustrated in FIGS. 1 to 3, the tractor 1 includes drivable andsteerable left and right front wheels 10 and drivable left and rightrear wheels 11, which function as a wheel-type driving device; a cabin13 that defines a boarding-type driver unit 12; an electronicallycontrolled diesel engine (hereinafter referred to as “engine”) 14including a common rail system; a speed change unit 15 that varies thepower from the engine 14; a fully hydraulic power steering mechanism 16that steers the left and right front wheels 10; a brake system 17 thatbrakes the left and right rear wheels 11; an electronically controlledclutch operation mechanism 19 that enables hydraulic operation of a workclutch that engages/disengages the power transmitted to the rotarytiller 6; an electrohydraulically controlled elevating drive mechanism20 that drives the rotary tiller 6 to raise/lower the rotary tiller 6;an electrohydraulically controlled roll-direction drive mechanism 21that drives the rotary tiller 6 in the roll direction; a vehicle-mountedcontrol system 22 including various control units; a vehicle statedetection device 23 that includes various sensors and switches fordetecting the various setting statuses and operation states of variousparts of the tractor 1; and a positioning unit 24 that measures thecurrent position, the current orientation, etc., of the tractor 1.

Note that the engine 14 may be an electronically controlled gasolineengine including an electronic governor. The power steering mechanism 16may be an electric power steering mechanism including an electric motor.

As illustrated in FIGS. 1 and 3 to 5, the driver unit 12 includesvarious operation levers, such as an accelerator lever and a speedchange lever; various operation pedals, such as an accelerator pedal 28and a clutch pedal 29; a steering wheel 30 that enables manual steeringof the left and right front wheels 10 via the power steering mechanism16; a seat 31 for a passenger; and a multi-touch type liquid crystalmonitor 32 serving as a display unit that displays various types ofinformation including information related to autonomous drive andenables an input operation.

As illustrated in FIG. 1, the cabin 13 is supported in a vibration-proofmanner by a front frame 34 disposed on the front side of the tractor 1and the speed change unit 15 also serving as a rear frame, viaanti-vibration rubber or the like. The engine 14 is supported in avibration-proof manner by the front frame 34 via vibration-proof rubberor the like. The engine 14 is covered by a bonnet 35 provided on thefront side of the tractor 1.

As illustrated in FIG. 2, the speed change unit 15 includes anelectronically controlled continuously variable transmission 36 thatvaries the power from the engine 14; an electrohydraulically controlledforward-reverse switching device 37 that switches the power that hasbeen varied by the continuously variable transmission 36 between forwardtravel and reverse travel; and a rear wheel differential that allowsdifference between the left and right rear wheels 11. The continuouslyvariable transmission 36 is implemented by an integrated hydrostaticmechanical transmission (I-HMT), which is an example of ahydromechanical continuously variable transmission having transmissionefficiency higher than that of a hydrostatic transmission (HST). Theforward-reverse switching device 37 includes a hydraulic clutch forinterrupting forward power, a hydraulic clutch for interrupting reversepower, and a solenoid valve for controlling the flow of oil to theclutches.

Note that, in place of the I-HMT, the continuously variable transmission36 may be implemented by a hydraulic mechanical transmission (HMT),which is an example of a hydromechanical continuously variabletransmission, a hydrostatic transmission (HST), a belt-type continuouslyvariable transmission, or the like. In place of the continuouslyvariable transmission 36, the speed change unit 15 may include anelectrohydraulically controlled stepped transmission including multiplehydraulic clutches for speed change and multiple solenoid valves forcontrolling the flow of oil to the clutches.

As illustrated in FIGS. 4 to 7, the brake system 17 includes left andright brake pedals 40 and a parking lever 41 provided in the driver unit12; left and right brakes 42 for respectively braking the left and rightrear wheels 11; left and right first linkage mechanisms 43 that link theleft and right brake pedals 40 and the left and right brakes 42,respectively, in conjunction with each other; a second linkage mechanism44 for parking that couples the parking lever 41 and the left and rightbrakes 42 in conjunction with each other; and an electrohydraulicallycontrolled first brake operating device 45 that operates the brake 42 onthe inner side of the turn in conjunction with steering of the left andright front wheels 10 by a set angle or more. When a passenger depressesat least one of the left and right the brake pedals 40, pulls up theparking lever 41 to a braking position, or steers the left and rightfront wheels 10 with the steering wheel 30 by a set angle or more, thebrake system 17 operates the corresponding brake(s) 42 to brake thecorresponding rear wheel(s) 11. Thus, when the left and right brakepedals 40 are depressed at the same time, the left and right brakes 42function as foot brakes that simultaneously brake the left and rightrear wheels 11. When the parking lever 41 is pulled up, the left andright brakes 42 function as parking brakes that simultaneously brake theleft and right rear wheels 11. When at least one of the brake pedals 40are depressed or when the left and right front wheels 10 are steered bya set angle or more, the left and right brakes 42 function as sidebrakes that brake the at least one of the rear wheels 11. An urgingmember, such as a compression spring, is disposed inside each of theleft and right brakes 42. The urging member urges each of the brakes 42to return the rear wheel 11 in a braking state in which the rear wheels11 is being braked to a released state in which the braking of the rearwheel 11 is released.

As illustrated in FIGS. 2 and 3, the vehicle-mounted control system 22includes an engine control unit 22A that performs control related to theengine 14; a speed change control unit 22B that performs control relatedto the continuously variable transmission 36, the forward-reverseswitching device 37, etc.; a steering control unit 22C that performscontrol related to the power steering mechanism 16, the first brakeoperating device 45, etc.; a work device control unit 22D that performscontrol related to work devices, such as the rotary tiller 6; a displaycontrol unit 22E that controls the display operation of the liquidcrystal monitor 32; an autonomous drive control unit 22F that performscontrol related to autonomous drive; and a non-volatile vehicle-mountedstorage unit 22G that sores preliminarily generated target travel routesfor autonomous drive. Each of the control units 22A to 22F isconstructed by an electronic control unit in which a microcontrollercontroller, etc., are integrated and various control programs. Asillustrated in FIG. 3, the autonomous drive control unit 22F is includedin the liquid crystal monitor 32 together with the display control unit22E. The control units 22A to 22F are connected such that they cancommunicate with each other via a controller area network (CAN).

As illustrated in FIG. 3, “vehicle state detection device 23” is a termcollectively referring to various sensors and switches provided in therespective parts of the tractor 1. The vehicle state detection device 23includes an accelerator sensor that detects the operation amount of theaccelerator lever and the accelerator pedal 28 from idling positions; aspeed change sensor that detects the operation amount of the speedchange lever from a zero speed position; a reverser sensor that detectsthe operation position of the reverser lever for switching betweenforward travel and reverse travel; left and right brake switches 25 (seeFIG. 3) that detect whether or not the left and right brake pedals 40are at depression release positions; left and right brake sensors 26(see FIG. 3) that detect the operation amount of the left and brakepedals 40 from depression release positions; a rotation sensor thatdetects the output rotation speed of the engine 14; a vehicle speedsensor that detects the vehicle speed of the trucker 1; and a steeringangle sensor that detects the steering angle of the front wheels 10.

The engine control unit 22A performs engine speed change control on thebasis of detection information from the accelerator sensor and detectioninformation from the rotation sensor. The engine speed change controlchanges the engine speed from an idling speed to a speed correspondingto the operation amount of the accelerator lever or the acceleratorpedal 28.

The speed change control unit 22B performs speed change control,forward-reverse switching control, brake speed change control, and othercontrol. The speed change control controls the operation of thecontinuously variable transmission 36 so that the vehicle speed of thetractor 1 varies to a speed corresponding to the operation amount of thespeed change lever on the basis of the detection information from thespeed change sensor, the detection information from the vehicle speedsensor, etc. The forward-reverse switching control switches the powertransmission state of the forward-reverse switching device 37 on thebasis of the detection information from the reverser sensor. The brakespeed change control controls the operation of the continuously variabletransmission 36 so that the vehicle speed of the tractor 1 decreasesfrom a speed corresponding to the operation amount of the speed changelever to a speed corresponding to the depression operation amount of theleft and right brake pedals 40 when the left and right brake pedals 40are simultaneously operated, on the basis of the detection informationfrom each of the brake sensors 26 and the detection information from thevehicle speed sensor. The speed change control includes a decelerationstop process of decelerating the continuously variable transmission 36to a zero speed state and stopping the driving of the tractor 1 when thespeed change lever is operated to a zero speed position. The brakingspeed change control includes a braking deceleration stop process ofdecelerating the continuously variable transmission 36 to a zero speedstate and thereby stopping the driving of the tractor 1 when the leftand right brake pedals 40 are depressed to a depression limit position.

As illustrated in FIGS. 4 to 7, the left and right brake pedals 40 ofthe brake system 17 are disposed next to each other in the right frontlower portion of the driver unit 12. The left and right brake pedals 40are urged by left and right extension springs 46 to return to depressionrelease positions. The left and right brake pedals 40 include bossportions 40A, pedal arm portions 40B, and pedal portions 40C. The bossportions 40A are supported by a rotary shaft 47 for pedal support thatextends in the left-right direction below and forward of the steeringwheel 30. The pedal arm portions 40B extend rearward and downward fromthe boss portions 40A.

The pedal portions 40C are attached to the free ends of the pedal armportions 40B. The boss portion 40A of the right brake pedal 40 rotatesrelative to the rotary shaft 47. The right brake pedal 40 includes alinkage arm portion 40D that extends forward and downward from the bossportion 40A. The boss portion 40A of the left brake pedal 40 rotatesintegrally with a linkage arm 48 via the rotary shaft 47. The linkagearm 48 is fixed to the left end of the rotary shaft 47.

As illustrated in FIGS. 4 and 5, the left and right brakes 42 areincluded in the speed change unit 15. Each of the left and right brakes42 includes an operation shaft 49 and an operation arm 50. The operationshaft 49 protrudes from the front end of the corresponding brake 42 in atransversely outward direction from the vehicle. The operation arm 50 isfixed to the protruding end of the operation shaft 49.

As illustrated in FIGS. 4 to 7, the left and right first linkagemechanisms 43 includes boss members 52, first linking rods 53, andsecond linking rods 54. The boss members 52 are rotatably supported byleft and right fixed shafts 51 that extend in the left-right directionbelow the rotary shaft 47. Each of the first linking rods 53 isvertically long and extends between a first arm portion 52A of thecorresponding boss members 52 and the linkage arm portion 40D of theright brake pedal 40 (or the linkage arm 48). The second linking rods 54are long in the front-back direction and extend between second armportions 52B of the boss members 52 and the operation arms 50 of thebrakes 42. The left first linkage mechanism 43 includes the rotary shaft47 and the linkage arm 48 described above. That is, the left and rightfirst linkage mechanisms 43 are of a rod linkage type in which the leftand right brake pedals 40 are respectively linked to the left and rightbrakes 42 via the first linking rods 53, the second linking rods 54,etc.

In the brake system 17 having the configuration described above, whenonly the right brake pedal 40 is depressed, the resulting operatingforce is transmitted to the operation arm 50 of the right brake 42 viathe right first linkage mechanism 43. As a result, the brake system 17switches to a right braking state in which the right rear wheel 11 isbraked by the right brake 42. When the depression operation of the rightbrake pedal 40 is then released, the right braking state switches to areleased state.

When only the left brake pedal 40 is depressed, the resulting operatingforce is transmitted to the operation arm 50 of the left brake 42 viathe left first linkage mechanism 43. As a result, the brake system 17switches to a left braking state in which the left rear wheel 11 isbraked by the left brake 42. When the depression operation of the leftbrake pedal 40 is then released, the left braking state switches to areleased state.

When the left and right brake pedals 40 are both depressed, theresulting operating force is transmitted to the operation arms 50 of theleft and right brakes 42 via the left and right first linkage mechanisms43. As a result, the brake system 17 switches to a braking state inwhich the left and right rear wheels 11 are respectively braked by theleft and right brakes 42. When the depression operation of the left andright brake pedals 40 is then released, the braking state switches to areleased state.

In this way, when the passenger manually drives the tractor 1, thepassenger can perform a brake-turn of the tractor 1 to reduce theturning radius of the tractor 1 by depressing the brake pedal 40 on theinner side of the turn while operating the steering wheel 30 in theturning direction. The passenger can depress both the left and rightbrake pedals 40 to brake and decelerate or brake and stop the tractor 1while the tractor 1 is kept in a straight-ahead orientation as a resultof the braking action of the left and right brakes 42 and the brakingspeed change control of the speed change control unit 22B describedabove.

As illustrated in FIGS. 6 to 12, the brake system 17 includes a couplingmechanism 55 that switches the left and right brake pedals 40 between acoupled state and a released state. In the coupled state, the left andright brake pedals 40 are coupled. In the released state, the coupledstate of the left and right brake pedals 40 is released. The couplingmechanism 55 includes an operation rod 56, a compression spring 57, aguide plate 58. The operation rod 56 is supported by the right brakepedal 40 so as to be movable in the left-right direction. Thecompression spring 57 urges the left end of the operation rod 56 tocause the operation rod 56 to protrude toward the left brake pedal 40.The guide plate 58 guides a guided portion 56A of the operation rod 56.The guide plate 58 has a J-shaped guide hole 58 a that guides the guidedportion 56A of the operation rod 56 between a couple position and arelease position. The left brake pedal 40 has a through-hole 40E (seeFIGS. 8, 11, and 12) into which the left end of the operation rod 56 ispassed when the guided portion 56A of the operation rod 56 is at thecouple position.

In the coupling mechanism 55 having the above-described configuration,when the operation rod 56 is operated so that the guided portion 56A ofthe operation rod 56 is positioned at the couple position, the left endof the operation rod 56 passes through the through-hole 40E of the leftbrake pedal 40. As a result, the left and right brake pedals 40 switchesto a coupled state, and the coupled state is held by the compressionspring 57. In the coupling mechanism 55, when the operation rod 56 isoperated so that the guided portion 56A of the operation rod 56 ispositioned at the release position, the left end of the operation rod 56is removed from the through-hole 40E of the left brake pedal 40. As aresult, the left and right brake pedals 40 switches to a released state,and the released state is held by the compression spring 57.

In this way, when the passenger manually drives the tractor 1 in afield, the passenger can operate the operation rod 56 and switch thecoupling mechanism 55 to a released state, to perform any necessarybrake-turns while driving in the field. When the passenger manuallydrives the tractor 1 outside the field, the passenger operates theoperation rod 56 and switches the coupling mechanism 55 to a coupledstate, to prevent the risk of performing unnecessary brake-turns whiledriving outside the field.

In the brake system 17, the parking lever 41 is disposed to the left ofthe seat 31 in the driver unit 12. The parking lever 41 is of atwo-position switching type that switches and holds two positions: anupper braking position and a lower release position. At the upperbraking position, the left and right brakes 42 are switched to a brakingstate. At the lower release position, the left and right brakes 42 areswitched to a released state. The operation of the parking lever 41 tothe braking position is detected by a parking switch included in thevehicle state detection device 23.

As illustrated in FIGS. 4 to 5, the second linkage mechanism 44 forparking includes left and right control cables 59, an equalizer unit 60,left and right link plates 61, and left and right linking pins 62. Theequalizer unit 60 couples one of the ends of inner cables of the leftand right control cables 59 to the parking lever 41. The left and rightlink plates 61 and the left and right linking pins 62, couple other endsof the left and right inner cables to the operation arms 50 of the leftand right brakes 42. That is, the second linkage mechanism 44 is of acable linkage type in which the parking lever 41 is linked to the leftand right brakes 42 via the left and right control cables 59, etc. Theleft and right link plates 61 have long holes through which the linkingpins 62 fixed to the left and right operation arms 50 are passed. Thelong holes function as allowance portions that allow displacement of theleft and right operation arms 50 relative to the left and right linkplates 61 in conjunction with the depressing operation of the left andright brake pedals 40.

In the brake system 17 having the above-described configuration, whenthe parking lever 41 is pulled up from the lower release position to theupper braking position and held in the braking position, the resultingoperating force is transmitted to the operation arms 50 of the left andright brakes 42 via the second linkage mechanism 44. As a result, theleft and right rear wheels 11 are respectively braked by the left andright brakes 42, and the braked state switches to a parking brake statein which the braking state is kept. When the parking lever 41 is thenpushed down from the upper braking position to the lower releaseposition and held in the release position, the parking brake state isswitched to a released state.

As illustrated in FIG. 6, vertically long holes 53 a are formed in thelower end portions of the first linking rods 53 in the left and rightfirst linkage mechanisms 43. Linking pins 63 fixed to the first armportions 52A of the boss members 52 are passed through the long holes 53a. As illustrated in FIGS. 3 to 5, in the left and right first linkagemechanisms 43, when the left and right brakes 42 are switched from thereleased state to the parking brake state as a result of the parkinglever 41 being pulled up, in conjunction with this switching, the leftand right second linking rods 54 are pulled rearward, and the second armportions 52B of the left and right boss members 52 swing to be displacedrearward. In conjunction with the swing displacement, the first armportions 52A of the left and right boss members 52 swing to be displacedupward. At this time, the long holes 53 a of the first linking rods 53function as allowance portions that allow the upward swing displacementof the left and right first arm portions 52A relative to the left andright first linking rods 53. This avoids a reduction in operability dueto the left and right brake pedals 40 interlocking and causing theoperation to become heavy when the left and right brakes 42 switch to aparking brake state as a result of the parking lever 41 being pulled up.

As illustrated in FIGS. 4 to 7, the first brake operating device 45 inthe brake system 17 includes a hydraulic unit 64 for automatic brake, apair of push-pull links 65, a pair of crank arms 66, left and rightcontrol cables 67, left and right link plates 68, and left and rightlinking pins 69. The hydraulic unit 64 includes two hydraulic cylindersand two solenoid valves corresponding to the left and right brakes 42.The push-pull links 65 are pushed and pulled by the hydraulic unit 64.The crank arms 66 swing around the longitudinal axis in conjunction withthe push-pull links 65.

The left and right control cables 67 extend from the crank arms 66toward the left and right boss members 52. The left and right linkplates 68 and the left and right linking pins 69 couple the front endsof inner cables 67A of the left and right control cables 67 to third armportions 52C of the left and right boss members 52. Oil from a hydraulicpump driven by power from the engine 14 is supplied to the hydraulicunit 64. The left and right link plates 68 have long holes 68 a throughwhich linking pins 69 fixed to the left and right third arm portions 52Care passed. The long holes 68 a function as allowance portions thatallow depression of the left and right brake pedals 40 or swingdisplacement of the left and right third arm portions 52C relative tothe left and right link plates 68 caused by a pulling operation of theparking lever 41.

As illustrated in FIG. 2, the brake system 17 includes the steeringcontrol unit 22C. When a selection switch for automatic brake includedin the driver unit 12 is operated to select an automatic brake mode, thesteering control unit 22C controls the operation of the hydraulic unit64 of the first brake operating device 45 on the basis of the detectionby the steering angle sensor and executes automatic brake control foroperating the left and right brakes 42. Under the automatic brakecontrol, the steering control unit 22C keeps each of the solenoid valvesof the hydraulic unit 64 in a discharge state in which oil is dischargedfrom each hydraulic cylinder while the steering angle of the left andright front wheels 10 is less than a set angle. In this way, thesteering control unit 22C keeps the left and right hydraulic cylindersin a contracted state and the left and right brakes 42 in a releasedstate. When the steering angle of the left and right front wheels 10reaches the set angle or more, the solenoid valves corresponding to therear wheel 11 on the inner side of the turn switch to a supply state inwhich oil is supplied to the hydraulic cylinders so as to extend thehydraulic cylinder corresponding to the rear wheel 11 on the inner sideof the turn and switch the brake 42 on inner side of the turn to abraking state.

During manual driving in which the automatic brake mode is selected, thebrake system 17 having the above-described configuration keeps the leftand right brakes 42 in a released state by the first brake operatingdevice 45 while the steering angle of the left and right front wheels 10based on the turning operation of the steering wheel 30 is smaller thanthe set angle. As a result, the turning state of the tractor 1 is keptin a normal turning state in which the tractor 1 turns with a turningradius corresponding to the steering angle of the left and right frontwheels 10. When the steering angle of the left and right front wheels 10based on the turning operation of the steering wheel 30 reaches the setangle or larger, the first brake operating device 45 switches the brake42 on the inner side of the turn to a braking state. As a result, theturning state of the tractor 1 switches to a brake-turn state in whichthe tractor 1 turns with a turning radius smaller than the turningradius in the normal turning state. Subsequently, when the steeringangle of the left and right front wheels 10 based on the turningoperation of the steering wheel 30 falls below the set angle, the firstbrake operating device 45 switches the left and right brakes 42 to areleased state. As a result, the turning state of the tractor 1 switchesto the normal turning state described above.

That is, when the passenger selects the automatic brake mode duringmanual driving by the passenger, and during turning in which the leftand right front wheels 10 are steered by the set angle or more, thebrake system 17 automatically switches the turning state of the tractor1 between the normal turning state and the brake-turn state on the basisof whether the angle of the left and right front wheels 10 being lessthan the set angle or larger than or equal to the set angle, without thepassenger depressing the brake pedal 40 on the inner side of the turn.As a result, the passenger can readily turn the tractor 1 with a smallradius by only turning the steering wheel 30.

As illustrated in FIG. 6, the lower ends of the first linking rods 53 ofthe left and right first linkage mechanisms 43 have long holes 53 a thatfunction as allowance portions, as described above. As a result, evenwhen the left and right brake pedals 40 are coupled by the couplingmechanism 55, the first brake operating device 45 can operate the brake42 on the inner side of the turn when the left and right front wheels 10are steered by the set angle or more, and switch the turning state ofthe tractor 1 to a brake-turn state.

The positioning unit 24 includes a satellite navigation device and aninertial measurement unit (IMU). The satellite navigation devicemeasures the current position and the current orientation of the tractor1 by using a global positioning system (GPS), which is an example of anavigation satellite system (NSS). The IMU includes a three-axisgyroscope, a three-direction acceleration sensor, etc., and measures theattitude, the orientation, and the like, of the tractor 1. Positioningmethods using a GPS include a differential GPS (DGPS) (which is arelative positioning method) and a real time kinematic GPS (RTK-GPS)(which is an interference positioning method). In the presentembodiment, an RTK-GPS suitable for measuring the position of a movingbody is employed. Accordingly, a reference station 73 that enablespositioning by the RTK-GPS is installed at a known location in theperiphery of the field, as illustrated in FIG. 1.

As illustrated in FIGS. 1 and 2, the tractor 1 and the reference station73 include GPS antennas 75 and 76, respectively, and communicationmodules 77 and 78, respectively. The GPS antennas 75 and 76 receiveradio waves transmitted from GPS satellites 74 (see FIG. 1). Thecommunication modules 77 and 78 enable wireless communication of variousdata items, including positioning data, between the tractor 1 and thereference station 73. In this way, the satellite navigation system ofthe positioning unit 24 can measure the current position and currentorientation of the tractor 1 with high accuracy on the basis of thepositioning data obtained by the GPS antenna 75 on the tractor sidereceiving radio waves from the GPS satellite 74 and the positioning dataobtained by the GPS antenna 76 on the base station side receiving radiowaves from the GPS satellite 74. The positioning unit 24, which isprovided with a satellite navigation device and an inertial measurementunit, enables highly accurate measurements of the current position, thecurrent orientation, and an attitude angle (yaw angle, roll angle, pitchangle) of the tractor 1.

In the tractor 1, the inertial measurement unit of the positioning unit24, the GPS antenna 75, and the communication module 77 are included inan antenna unit 79 illustrated in FIG. 1. The antenna unit 79 isdisposed at the center of the upper portion in the left and rightdirection on the front side of the cabin 13.

As illustrated in FIG. 2, the mobile communication terminal 3 includes aterminal control unit 80 and a communication module 81. The terminalcontrol unit 80 includes an electronic control unit on which amicrocontroller, etc., are integrated and various control programs. Thecommunication module 81 enables wireless communication of various dataitems including the positioning data with the communication module 77 onthe tractor side. The terminal control unit 80 includes a displaycontrol unit 80A, a travel route generating unit 80B, and a non-volatileterminal storage unit 80C. The display control unit 80A controls theoperation of a display unit 4. The travel route generating unit 80Bgenerates a target travel route for autonomous drive. The non-volatileterminal storage unit 80C stores the target travel route generated bythe travel route generating unit 80B.

The target travel route includes various route section, such as multiplework route sections disposed in parallel at regular intervalscorresponding to the work width of the tractor 1 and multiple non-workturning route sections connecting the end and start of adjacent workroute sections in the order of travel. The target travel route alsoincludes proper engine speed, proper vehicle speed, traveling directionof the tractor 1, front wheel steering angle at the turning routesection, stop position of the tractor 1, etc., that are set inaccordance with the drive mode of the tractor 1 in the various turningroute sections.

As illustrated in FIG. 3, detection information from various sensors andswitches included in the vehicle state detection device 23 is input tothe autonomous drive control unit 22F via the speed change control unit22B, the steering control unit 22C, etc. In this way, the autonomousdrive control unit 22F can monitor various setting states of the tractor1 and operating states of the various parts.

When the display unit 4 of the mobile communication terminal 3 isoperated by a user, such as the passenger or an administrator outside ofthe vehicle, and the start of autonomous drive is instructed while thedrive mode of the tractor 1 is switched to an autonomous drive mode, theautonomous drive control unit 22F starts autonomous drive control tocause autonomous drive of the tractor 1 along the target travel routewhile the positioning unit 24 acquires the current position of thetractor 1.

The autonomous drive control by the autonomous drive control unit 22Fincludes an autonomous control process for the engine in which a controlcommand for autonomous drive related to the engine 14 is sent to theengine control unit 22A; an autonomous control process for speed changein which a control command for autonomous drive related to thecontinuously variable transmission 36, the forward-reverse switchingdevice 37, etc., is sent to the speed change control unit 22B; anautonomous control process for steering in which a control command forautonomous drive related to steering is sent to the steering controlunit 22C; and an autonomous control process for work in which a controlcommand for autonomous drive related to work devices, such as the rotarytiller 6, is sent to the work device control unit 22D.

In the autonomous control process for the engine, the autonomous drivecontrol unit 22F sends, to the engine control unit 22A, an engine speedchange command for instructing a change in engine speed on the basis ofthe proper engine speed or the like included in the target travel routeand an engine stop command for instructing the engine 14 to stop on thebasis of the establishment of an engine stop condition.

In the autonomous control process for speed change, the autonomous drivecontrol unit 22F sends, to the speed change control unit 22B, a speedchange operation command for instructing the continuously variabletransmission 36 to change speed on the basis of the proper vehicle speedincluded in the target travel route, a forward-reverse switching commandfor instructing the forward-reverse switching device 37 to switchbetween forward travel and reverser travel on the basis of the traveldirection of the tractor 1 included in the target travel route, aneutral switching command for instructing the forward-reverse switchingdevice 37 to switch to a neutral state on the basis of the establishmentof a travel power cutoff condition.

In the autonomous control process for steering, the autonomous drivecontrol unit 22F sends, to the steering control unit 22C, a steeringcommand for instructing the steering of the left and right front wheels10 on the basis of the front wheel steering angles or the like in thetarget travel route.

In the autonomous control process for work, the autonomous drive controlunit 22F sends, to the work device control unit 22D, a work startcommand for instructing the rotary tiller 6 to switch to a work state onthe basis of the work state point included in the target travel routeand a work stop command for instructing the rotary tiller 6 to switch toa non-work state on the basis of the work stop point included in thetarget travel route.

Note that, in regard or the engine stop condition and the travel powercutoff condition described above, the autonomous drive control unit 22Fdetermines that the engine stop condition and the travel power cutoffcondition have been established when an error is detected on the basisof various items of information from the vehicle state detection device23, etc. The error is, for example, an error of the speed change controlunit 22B, such as a speed change control failure in which the propervehicle speed differs from the vehicle speed of the tractor 1, or anerror in the CAN communication with the speed change control unit 22Band the steering control unit 22C.

The engine control unit 22A performs automatic engine speed changecontrol, automatic engine stop control, etc., in accordance with variouscontrol commands related to the engine 14 sent from the autonomous drivecontrol unit 22F in the autonomous control process for the engine. Theautomatic engine speed change control automatically changes the enginespeed. The automatic engine stop control automatically stops the engine14.

The speed change control unit 22B performs automatic speed changecontrol, automatic forward-reverse switching control, automatic neutralswitching control, etc., in accordance with various control commandsrelated to the continuously variable transmission 36, theforward-reverse switching device 37, etc., sent from the autonomousdrive control unit 22F in the autonomous control process for speedchange. The automatic speed change control automatically controls theoperation of the continuously variable transmission 36. The automaticforward-reverse switching control automatically controls the operationof the forward-reverse switching device 37. The automatic neutralswitching control automatically switches the forward-reverse switchingdevice 37 to a neutral state so that the power transmitted to the leftand right front wheels 10 and the left and right rear wheels 11 are cutoff. The automatic speed change control includes an automaticdeceleration stop process of decelerating the continuously variabletransmission 36 to a zero state and stopping the driving of the tractor1, for example if the proper vehicle speed included in the target travelroute is zero.

The steering control unit 22C performs automatic steering control,automatic brake turning control, etc., in accordance with a steeringcommand sent from the autonomous drive control unit 22F in theautonomous control process for steering. The automatic steering controlcontrols the operation of the power steering mechanism 16 and steers theleft and right front wheels 10. The automatic brake turning controloperates the first brake operating device 45 and operates the brake 42on the inner side of the turn if the left and right front wheels 10 aresteered at a set angle or more.

The work device control unit 22D performs automatic work start control,automatic work stop control, etc., in accordance with various controlcommands related to the rotary tiller 6 sent from the autonomous drivecontrol unit 22F in the autonomous control process for work. Theautomatic work start control controls the operation of the elevatingdrive mechanism 20 and the clutch operation mechanism 19, lowers therotary tiller 6 to a work height, and operates the rotary tiller 6. Theautomatic work stop control stops the rotary tiller 6 and raises therotary tiller 6 to a non-work height. In a work state in which therotary tiller 6 is lowered to a work height and operated, the workdevice control unit 22D performs automatic tillage depth control andautomatic roll angle maintenance control. The automatic tillage depthcontrol controls the operation of the elevating drive mechanism 20 andkeeps the tillage depth made by the rotary tiller 6 to a set depth onthe basis of the detection of a tillage sensor that detects a tillagedepth of the rotary tiller 6. The automatic roll angle maintenancecontrol controls the operation of the roll-direction drive mechanism 21and keeps the tilt of the rotary tiller 6 in the roll direction to a setorientation (for example, a horizontal orientation) on the basis of atilt sensor that detects the roll angle of the tractor 1 and detectionof an acceleration sensor of an inertia measuring unit.

That is, the above-described autonomous drive unit 2 includes a powersteering mechanism 16, a clutch operation mechanism 19, an elevatingdrive mechanism 20, a roll-direction drive mechanism 21, avehicle-mounted control system 22, a vehicle state detection device 23,a positioning unit 24, and a communication module 77. The properoperation of these components enables accurate autonomous drive of thetractor 1 along the target travel route and proper tillage by the rotarytiller 6. In case of an error in the speed change control unit 22B ofthe tractor 1 or an error in the CAN communication, the driving of thetractor 1 can be automatically stopped.

As illustrated in FIGS. 2, 4, 5, and 8 to 11, the brake system 17includes an electric second brake operating device 100 that operates theleft and right brake pedals 40 coupled by the coupling mechanism 55 soas to operate the left and right brakes 42 as safety brakes. Asillustrated in FIG. 3, the autonomous drive control unit 22F includes asafety brake function unit 22Fa that controls the operation of thesecond brake operating device 100 so as to cause the left and rightbrakes 42 to function as safety brakes.

As illustrated in FIGS. 8 to 11, the second brake operating device 100is disposed on the right side of the right brake pedal 40 in the driverunit 12. The second brake operating device 100 includes an operated body101, an electric actuator 102, and an allowance portion 103. Theoperated body 101 is coupled to the right brake pedal 40. The electricactuator 102 operates the operated body 101 in the front-rear direction.The allowance portion 103 allows displacement of the right brake pedal40, etc., relative to the electric actuator 102 between the right brakepedal 40 and the electric actuator 102, in conjunction with thedepression of the brake pedal 40.

As illustrated in FIGS. 8 to 12, the operated body 101 includes a firstmember 104, a second member 105, a damper 107, and a link plate 108. Thefirst member 104 and a second member 105 are coupled to the pedal armportions 40B of the right brake pedal 40. The damper 107 is swingablycoupled to the second member 105 in the vertical direction via acoupling pin 106 extending in the left-right direction. The link plate108 is coupled to the damper 107 so that the position of the link plate108 is adjustable in the front-back direction. A long hole 108 a isformed in the link plate 108. The long hole 108 a extends in thefront-back direction and functions as the allowance portion 103. Theelectric actuator 102 is an electric motor including a worm reducer102A. The electric motor 102 is switched between a forward rotationoperation state, a reverse rotation operation state, and an operationstop state by the control and operation of the steering control unit22C. In the forward rotation operation state, forward rotation power isoutput. In the reverse rotation operation state, reverse rotation poweris output. In the operation stop state, the output of rotation powerstops. A deceleration gear set 111 and a linking pin 112 are disposedbetween the operated body 101 and the worm reducer 102A of the electricmotor 102. The deceleration gear set 111 includes a small-diameter inputgear 109 and a large-diameter output gear 110 and further reduce thepower from the worm reducer 102A. The linking pin 112 links the outercircumference of the output gear 110 of the deceleration gear set 111and the operated body 101 via the allowance portion 103. The linking pin112 is fixed to the outer circumference of the output gear 110 whilebeing passed through the long hole 108 a in the link plate 108. Thelinking pin 112 moves from a non-operating position (see FIGS. 8 to 11)to a maximum operation position (see FIG. 12), by the forward rotationpower from the electric motor 102, and moves from the maximum operationposition to the non-operating position by the reverse rotation powerfrom the electric motor 102. At the non-operating position, the rightbrake pedal 40 (the right brake 42) is not operated. At the maximumoperation position, the operation amount of the right brake pedal 40(the right brake 42) is maximized. The non-operating position of thelinking pin 112 is set so that the linking pin 112 is positioned at thefront end of the long hole 101 a when the right brake pedal 40 is at adepression release position.

With the above-described configuration, when the right brake pedal 40 isdepressed, the forward movement of the operated body 101 relative to thelinking pin 112 caused by the depression operation is allowed by theallowance of the long hole 108 a (the allowance portion 103) of the linkplate 108. As a result, when the right brake pedal 40 or the left andright brake pedals 40 are depressed while the tractor 1 is manuallydriven by the passenger, the right brake 42 or the left and right brakes42 can be braked in conjunction with the depression by the action of theallowance portion 103, without hinderance by the electric motor 102.

By the electric motor 102 switching to the forward rotation operationstate in a state in which the left and right brake pedals 40 are coupledby the coupling mechanism 55, the left and right brake pedals 40 can bemoved to a depression limit position, and thereby the left and rightbrakes 42 can be switched to the braking state. Switching of theelectric motor 102 to the reverse rotation operation state moves theleft and right brake pedals 40 to the depression release position. As aresult, the left and right brakes 42 can be switched to a releasedstate.

A first limit switch 113 is disposed at the non-operating position ofthe linking pin 112. The first limit switch 113 detects the linking pin112 reaching the non-operating position by the operation of the electricmotor 102. A second limit switch 114 is disposed at the maximumoperation position of the linking pin 112. The second limit switch 114detects the linking pin 112 reaching the maximum operation position bythe operation of the electric motor 102. When the left and right brakepedals 40 are coupled by the coupling mechanism 55, the non-operatingposition of the linking pin 112 is a release position at which thebraking by the left and right brakes 42 is released, and the maximumoperation position of the linking pin 112 is a braking position at whichthe braking by the left and right brakes 42 is maximized. In this way,the first limit switch 113 functions as a release switch that detectsthe linking pin 112 reaching the release position by the operation ofthe electric motor 102. The second limit switch 114 functions as abraking switch that detects the linking pin 112 reaching the brakingposition of the linking pin 112 by the operation of the electric motor102. The release switch 113 and the braking switch 114 function as afirst operation sensor for detecting the operation of the electric motor102.

As illustrated in FIG. 3, the release switch 113 and the braking switch114 are included in the vehicle state detection device 23 together withthe left and right brake switches 25, the left and right brake sensors26, etc. The vehicle state detection device 23 includes a couplingswitch that is turned on when the left and right brake pedals 40 arecoupled by the coupling mechanism 55.

When the left and right brake switches 25 detect the left and rightbrake pedals 40 at the depression release positions, and when thedetection values of the left and right brake sensors 26 indicate thedepression release positions of the left and right brake pedals 40 whilethe coupling switch is turned on, the steering control unit 22C candetect the released state of the left and right brakes 42. When the leftand right brake switches 25 do not detect the left and right brakepedals 40 at the depression release positions, and when the detectionvalues of the left and right brake sensors 26 indicate the maximumdepression positions of the left and right brake pedals 40 while thecoupling switch is turned on, the steering control unit 22C can detectthe braking state of the left and right brakes 42. In other words, theleft and right brake switches 25 and the left and right brake sensors 26function as a second operation sensor that detects the operation of theleft and right brakes 42 when the left and right brake pedals 40 arecoupled by the coupling mechanism 55.

The steering control unit 22C having the above-described configurationcontrols the operation of the electric motor 102 on the basis of thedetection of the left and right brake switches 25, the detection valuesof the left and right brake sensors 26, the detection of the releaseswitch 113, and the detection of the braking switch 114, while the leftand right brake pedals 40 are coupled by the coupling mechanism 55.Through such control, the steering control unit 22C can certainly switchthe left and right brakes 42 from a released state to a braking state,and from a braking state to a released state.

As illustrated in FIGS. 8 to 12, the second brake operating device 100includes a housing case 116 that is fixed to a floor plate (an exampleof a fixing portion of the vehicle) 38 of the driver unit 12. Thehousing case 116 has a base plate 117, a left case body 118, a firstsupport plate 119, a second support plate 120, and a right case body121. The base plate 117 is detachably bolted to the floor plate 38. Theleft case body 118 is bolted to the floor plate 38 and the base plate117. The first support plate 119 is welded to the inner face of the leftcase body 118. The second support plate 120 is fixed to the sidewall ofthe left case body 118 with a predetermined gap provided therebetween.The right case body 121 is bolted to the left case body 118. In thehousing case 116, a storage space is formed between the left case body118 and the right case body 121.

In the housing case 116, three stepped bolts 122 extending from thesidewall of the left case body 118 in the right direction are fixed tothe left case body 118. The second support plate 120 is fixed to thesidewall of the left case body 118 via the stepped bolts 122. Among thethree stepped bolts 122, the stepped bolt 122 positioned near the centerof the sidewall is used as a support shaft 123 to rotatably support theoutput gear 110. A guide hole 118 a for guiding the linking pin 112between the release position and the braking position is formed in thesidewall of the left case body 118 in an arc shape centered about thesupport shaft 123. The electric motor 102 is fixed to the first supportplate 119 with three bolts 124. The input gear 109 that meshes with theoutput gear 110 is fixed to the output shaft of the worm reducer 102A ofthe electric motor 102. One end portion of the second support plate 120functions as a first receiving portion 120A for receiving the linkingpin 112 having reached the release position. The other end portion ofthe second support plate 120 functions a second receiving portion 120Bfor receiving the linking pin 112 having reached the braking position.The release switch 113 is fixed to the one end portion of the secondsupport plate 120, and the braking switch 114 is fixed to the other endportion of the second support plate 120.

In the second brake operating device 100 having the above-describedconfiguration, the electric motor 102, the deceleration gear set 111,the release switch 113, the braking switch 114, etc., are housed in thehousing case 116. In this way, the housing case 116, the electric motor102, the deceleration gear set 111, the release switch 113, the brakingswitch 114, etc., can be detachably attached to the floor plate 38 in anintegrated state as a drive unit. After the driver unit has beenattached, the operated body 101 coupled to the right brake pedal 40 andthe output gear 110 of the drive unit are linked via the allowanceportion 103 and the linking pin 112 so that the operated body 101 can beoperated by the electric motor 102. In this way, the second brakeoperating device 100 can be installed to the driver unit 12 so that theleft and right brakes 42 can be operated by the second brake operatingdevice 100.

In other words, the second brake operating device 100 can be readilyinstalled to the driver unit 12 without significantly modifying theconfiguration of the driver unit 12. In this way, the second brakeoperating device 100 can be retrofitted to the tractor 1. As a result,the second brake operating device 100 can be readily installed to thetractor 1. Also, maintenance, such as replacement of the second brakeoperating device 100, can be readily performed when a problem occurs inthe second brake operating device 100.

As illustrated in FIGS. 8 to 10, the first receiving portion 120A andthe second receiving portion 120B of the second support plate 120function as a movement restrictor that restrict the movable range of thelinking pin 112 between the release position and the braking position.The movable range of the linking pin 112 is set to a range in which thelinking pin 112 moves between the release position and the brakingposition across an imaginary straight line L1. The imaginary straightline L1 passes through the coupling pin 106 and the support shaft 123.The coupling pin 106 is the coupling point of the operated body 101 withrespect to the right brake pedal 40. The support shaft 123 is therotation center of the output gear 110.

With the above-described configuration, when the second brake operatingdevice 100 operates the left and right brakes 42, the forward rotationpower from the electric motor 102 is first transmitted to the outputgear 110 to rotate the output gear 110 in the braking direction, andthereby, the linking pin 112 moves from the release position to thebraking position while following an arc. At this time, a braking force Aof the left and right brakes 42 increases in accordance with the amountof movement of the linking pin 112 passing through a play regionincluding the release position and reaching the braking position, asillustrated in FIG. 13. An operating load B applied to the electricmotor 102 increases as the linking pin 112 approaches the imaginarystraight line L1 in a first movable range of the linking pin 112 afterpassing through the play region until crossing the imaginary straightline L1 because the reaction force from various parts, such as frictionplates, generated inside the left and right brakes 42 increases with anincrease in the braking force A of the left and right brakes 42, and theleft and right brake pedals 40 are urged to return to the depressionrelease position by the tension of the left and right extension springs46. On the contrary, as the linking pin 112 approaches the imaginarystraight line L1, the angle θ (see FIG. 11) between the line L2connecting the linking pin 112 and the rotation center of the outputgear 110 and the operated body 101 becomes smaller. As a result, thereaction force from the left and right brakes 42 and the tension fromthe left and right extension springs 46 applied to the left and rightbrake pedals 40 do not readily act as forces for returning the linkingpin 112 to the release position. Thus, the amount of increase inoperating load B applied to the electric motor 102 decreases.Thereafter, when the linking pin 112 crosses the imaginary straight lineL1, the reaction force from the left and right brakes 42 and the tensionof the left and right extension springs 46 shift to assisting thebraking operation of the left and right brakes 42 by the electric motor102. Therefore, the operating load B applied to the electric motor 102decreases as the linking pin 112 moves away from the imaginary straightline L1 and approaches the braking position in a second movable range ofthe linking pin 112 after crossing the imaginary straight line L1 untilreaching the braking position. With the linking pin 112 reached at thebraking position, the linking pin 112 is urged to move in the brakingdirection by the reaction force from the left and right brakes 42 andthe tension of the left and right extension springs 46 while themovement of the linking pin 112 in the braking direction is restrictedby the second receiving portion 120B. In this way, for example, if theworm reducer 102A of the electric motor 102 is damaged or the outputgear 110 is defective when the linking pin 112 reaches the secondmovable region after crossing the imaginary straight line L1, thelinking pin 112 moves to and is held at the braking position by thereaction force from the left and right brakes 42 and the tension of theleft and right extension springs 46. As a result, the left and rightbrakes 42 can be kept in a braking state, and the tractor 1 can be keptin a braking stop state.

As a result, as the operating load B applied to the electric motor 102is reduced during the braking operation of the left and right brakes 42by the second brake operating device 100, the tractor 1 can be kept atthe braking stop state while the tractor 1 is braked and stopped by theoperation of the second brake operating device 100, regardless of adamage to the worm reducer 102A of the electric motor 102 and a defectin the output gear 110.

As illustrated in FIG. 3, the safety brake function unit 22Fa monitorsthe operating state of the components of the tractor 1 and thecommunication state with the components on the basis of various items ofdetection information from the vehicle state detection device 23received via the speed change control unit 22B, the steering controlunit 22C, etc. In the autonomous drive mode, when the safety brakefunction unit 22Fa detects an error inside the vehicle on the basis ofdetection information from the vehicle state detection device 23 orobtains an emergency stop command from the mobile communication terminal3 or an emergency stop remote control 90 (see FIG. 2), which is anexample of a wireless communication device, the safety brake functionunit 22Fa performs emergency stop control to control the operation ofthe electric motor 102 and switch the left and right brakes 42 from areleased state to a braking state. For this reason, the tractor 1includes an emergency stop communication antenna 91 for receiving anemergency stop command sent from the emergency stop remote control 90,as illustrated in FIG. 2.

An error inside the vehicle may include a drop in the engine speed to orbelow a set lower limit that may lead to engine stall, a control failuresuch as the vehicle speed of the tractor 1 deviating from the propervehicle speed under the automatic speed change control by the speedchange control unit 22B, and a communication failure in the CANcommunication due to disconnection, etc.

Note that the error inside the vehicle may include a control failuresuch as a deviation of the current position of the tractor 1 measured bythe positioning unit 24 from the target travel route under the automaticsteering control by the steering control unit 22C.

Therefore, under the emergency stop control, the safety brake functionunit 22Fa performs a first determination process (step #1), a seconddetermination process (step #2), a third determination step (step #3),and a fourth determination process (step #4), as illustrated in theflowchart in FIG. 14. In the first determination process (step #1), thesafety brake function unit 22Fa determiners whether or not the enginespeed has dropped to or below a set lower limit that may lead to enginestall on the basis of the detection information from a rotation sensorfor engine speed detection included in the vehicle state detectiondevice 23. In the second determination process (step #2), the safetybrake function unit 22Fa determines whether or not a control failure,such as the vehicle speed of the tractor 1 deviating from the propervehicle speed, has occurred in the speed change control unit 22B on thebasis of the detection information from a vehicle sensor or the likeincluded in the vehicle state detection device 23. In the thirddetermination step (step #3), the safety brake function unit 22Fadetermines whether or not a communication failure has occurred in theCAN communication on the basis of the detection information from anerror detector for CAN communication included in the vehicle statedetection device 23. In the fourth determination process (step #4), thesafety brake function unit 22Fa determines whether or not an emergencystop command has been obtained from the mobile communication terminal 3or the emergency stop remote control 90. When the engine speed decreasesin the first determination process (step #1), when a control failure hasoccurred in the speed change control unit 22B in the seconddetermination process (step #2), when a communication failure hasoccurred in the CAN communication in the third determination process(step #2), or when an emergency stop command is obtained in the fourthdetermination process (step #4), an emergency stop process (step #5)that causes an emergency stop of the tractor 1 and an emergency stopnotification process (step #6) that provides a notification about theemergency stop are performed.

In the emergency stop process, the safety brake function unit 22Fa sendsan engine stop command to the engine control unit 22A and sends a safetybrake operation command for operating the left and right brakes 42 assafety brakes to the steering control unit 22C. In the emergency stopprocess, the safety brake function unit 22Fa deselects the autonomousdrive mode and causes a transition of the drive mode from the autonomousdrive mode to the manual drive mode. In the emergency stop notificationprocess, the safety brake function unit 22Fa operates a notificationdevice 83 (see FIG. 2), such as an indicator light for emergency stop,which is provided in the tractor 1, and sends an emergency stopnotification command to the mobile communication terminal 3.

The engine control unit 22A performs the above-described automaticengine stop control in response to the engine stop command from theautonomous drive control unit 22F and automatically stops the engine 14.

The steering control unit 22C brakes and stops the tractor 1 byoperating the electric motor 102 and switching the left and right brakes42 from a released state to a braking state in response to the safetybrake operation command from the safety brake function unit 22Fa.

The mobile communication terminal 3 performs the emergency stopnotification process of switching the display screen of the display unit4 to an emergency stop notification screen in response to the emergencystop notification command from the autonomous drive control unit 22F.

With this configuration, the left and right brake pedals 40 are coupledwith the coupling mechanism 55 when the tractor 1 is autonomouslydriven, so as to automatically stop the engine 14 and automaticallyoperate the left and right brakes 42 as safety brakes, thereby to brakeand stop the tractor 1 in case an error occurs inside the vehicle, suchas a decrease in the engine speed to or below a set lower limit, acontrol failure in the speed change control unit 22B, or a communicationfailure in the CAN communication.

As a result, in case any of the above-mentioned errors occurs inside thevehicle in the autonomous drive mode, the tractor 1 can be quicklybraked and stopped and kept in the braking stop state, even when thetractor 1 is in an unmanned drive state in which the tractor 1 isautonomously driven. When the rotary tiller 6 is operating, the engine14 can be stopped, and the operation of the rotary tiller 6 can also bestopped.

Unlike the electrohydraulically controlled first brake operating device45, which operates the left and right brakes 42 by the oil from thehydraulic pump driven by the engine power, the electric motor 102 canoperate the left and right brakes 42 and keep a braking state, evenafter the engine 14 has stopped and the hydraulic pressure has dropped.In this way, the tractor 1 can be kept in the braking stop state evenafter the engine control unit 22A has stopped the engine 14 in responseto an engine stop command from the autonomous drive control unit 22F.

As a result, it is possible to avoid the risk of the tractor 1unexpectedly descending from an emergency stop position of the tractor 1located on a slope tilting in the travel direction of the tractor 1.

After the emergency stop process described above has been performed, thesafety brake function unit 22Fa performs the emergency stop releaseprocess if the power is turned off by operating to turn off a key switch(an example of an operating tool) 84 (see FIG. 2) provided in the driverunit 12 and then turned on again by turning on the key switch 84. In theemergency stop release process, the safety brake function unit 22Fasends an engine stop release command to the engine control unit 22A andsends a safety brake release command to the steering control unit 22C.The engine control unit 22A permits the activation of the engine 14 inresponse to the engine stop release command from the safety brakefunction unit 22Fa. The steering control unit 22C releases the brakingstop of the tractor 1 by operating the electric motor 102 and switchingthe left and right brakes 42 from the braking state to a released statein response to the safety brake release command from the safety brakefunction unit 22Fa.

In this way, when the tractor 1 is urgently stopped under the control ofthe safety brake function unit 22Fa, the tractor 1 can be kept in theemergency stop state until the power that was turned off is turned onagain by the operation of the key switch 84. When the power is turned onagain by the operation of the key switch 84, the activation of theengine 14 is permitted, and the braking stop of the tractor 1 isreleased. In this way, the passenger can activate the engine 14, and thetractor 1 can be manually driven by the passenger. As a result, thetractor 1 can be moved to a safe place or a repair shop by manualdriving.

As illustrated in FIG. 15, a home screen 32A of the liquid crystalmonitor 32 displays a mode selection button (mode selector) 32 a thatenables selection of the autonomous drive mode and the like. When theautonomous drive mode is selected through operation of the modeselection button 32 a, the autonomous drive control unit 22F performs acondition establishment determination process of determining whether ornot all conditions for the transition of the drive mode of the tractor 1from the manual drive mode to the autonomous drive mode are established.If all of the conditions are established, the autonomous drive controlunit 22F causes the drive mode of the tractor 1 to transition from themanual drive mode to the autonomous drive mode, and notifies the mobilecommunication terminal 3 about the transition of the drive mode of thetractor 1 to the autonomous drive mode so as to enable the start ofautonomous drive by operation of the mobile communication terminal 3. Ifall of the conditions are not established, the autonomous drive controlunit 22F continues the condition establishment determination processuntil all of the conditions are established or the cancel buttondisplayed on the liquid crystal monitor 32 is operated.

The conditions for the transition of the drive mode to the autonomousdrive mode includes the completion of various setting operationsrequired for the autonomous drive of the tractor 1, such as setting theengine speed for autonomous drive through an operation of theaccelerator lever and setting the vehicle speed for autonomous drivethrough an operation of the speed change lever, as well as theconfirmation of a normal operation during an initial check (operationconfirmation process) for checking whether or not the left and rightbrakes 42 operate normally as safety brakes. In other words, in order totransition the driving mode to the autonomous drive mode, it isnecessary to perform an initial check in advance and confirm that theleft and right brakes 42 operate normally as the safety brakes.

An initial check is included in the control operation of the safetybrake function unit 22Fa. When the normal operation has been confirmedthrough an initial check, the safety brake function unit 22Fa has causeda transition to an initial check completed state (operation checkedstate: “Check_OK” in FIG. 24). A valid period is set for the initialcheck completed state. In this embodiment, the valid period for theinitial check completed state is set to within the same day. Therefore,the safety brake function unit 22Fa stores the transition date in thevehicle-mounted storage unit 22G at the time of the transition to theinitial check completed state.

Note that the valid period for the initial check completed state may beset to various settings: for example, several days from the transitiondate, several hours from the transition time, or the time of driving aset distance from the distance at the transition.

The execution of an initial check is premised on the establishment ofall of first to ninth conditions described below (conditions forstarting the operation check process).

First condition: the steering control unit 22C controlling the operationof the electric motor 102 that causes the left and right brakes 42 tofunction as safety brakes is normal.

Second condition: the speed change control unit 22B that monitors thedetection information from the left and right brake switches 25, theleft and right brake sensors 26, etc., is normal.

Third condition: the CAN communication with the steering control unit22C is normal.

Fourth condition: the CAN communication with the speed change controlunit 22B is normal.

Fifth condition: the left and right brake pedals 40 are detected to beat the depression release positions on the basis of the detectioninformation received from the left and right brake switches 25 and theleft and right brake sensors 26 via the speed change control unit 22B.

Sixth condition: the reverser lever is detected to be in a neutralposition on the basis of the detection information received from thereverser sensor via the speed change control unit 22B.

Seventh condition: the parking lever 41 is detected to not be at thebraking position on the basis of the detection information received fromthe parking switch via the speed change control unit 22B.

Eighth condition: the left and right brake pedals 40 are detected to becoupled by the coupling mechanism 55 on the basis of the detectioninformation received from the coupling switch via the steering controlunit 22C.

Ninth condition: the vehicle speed is detected to be zero on the basisof the detection information received from the vehicle speed sensor viathe speed change control unit 22B.

The state transitions of the safety brake function unit 22Fa during aninitial check will be described below with reference to FIGS. 15 to 25.

The safety brake function unit 22Fa enters an initial state (“Start” inFIG. 24) when the power is turned on by turning on the key switch 84(see FIG. 2). In the initial state, a period elapse determinationprocess is performed to determine whether or not the initial checkcompleted state has the valid period.

In the initial state, if the release switch 113 has detected the linkingpin 112 operated by the electric motor 102 at the release position, andif the braking switch 114 has detected the linking pin 112 at thebraking position, the safety brake function unit 22Fa determines that anerror has occurred in any one of the electric motor 102, the releaseswitch 113, and the braking switch 114 and causes a transition to anerror detection state (“Err_Detection” in FIG. 24).

In the initial state, if the initial check completed state has continuedfor more than the valid period while the release switch 113 has notdetected the linking pin 112 at the release position, the safety brakefunction unit 22Fa causes a transition to a brake release returnoperation state (“Rev_Start” in FIG. 24) and instructs the steeringcontrol unit 22C to release the left and right brakes 42 by theoperation of the electric motor 102. In this way, the steering controlunit 22C releases the left and right brakes 42 by the operation of theelectric motor 102. If the safety brake function unit 22Fa has beenoperating the left and right brakes 42 as safety brakes while the keyhas been previously turned on, the left and right brakes 42 can bereturned to a released state through the release operation.

If the autonomous drive mode is selected through the operation of themode selection button 32 a on the home screen 32A illustrated in FIG. 15in the initial state, the safety brake function unit 22Fa performs apre-condition determination process of determining whether or not thefirst to ninth conditions are all established.

If any one of the conditions 1 to 9 is not established in thepre-condition determination process, the safety brake function unit 22Facauses a transition to a pre-condition establishment standby state(“Check_PreStandby” in FIG. 24) and causes a transition of the displayscreen of the liquid crystal monitor 32 to a safety brake checkselection screen 32B illustrated in FIG. 16.

If all of the conditions 1 to 9 are established in the pre-conditiondetermination process, the safety brake function unit 22Fa causes atransition to an initial check standby state (“Check_Standby” in FIG.24) and causes a transition of the display screen of the liquid crystalmonitor 32 to the safety brake check selection screen 32B illustrated inFIG. 16.

If the release switch 113 has not detected the linking pin 112 at therelease position within the valid period of the initial check completedstate, in the initial state, the safety brake function unit 22Fa causesa transition to a checked brake release return operation state (“OK_Rev”in FIG. 24) and instructs the steering control unit 22C to release theleft and right brakes 42 by the operation of the electric motor 102. Inthis way, the steering control unit 22C releases the left and rightbrakes 42 by the operation of the electric motor 102. If the safetybrake function unit 22Fa has been operating the left and right brakes 42as safety brakes while the key has been previously turned on, the leftand right brakes 42 can be returned to a released state through therelease operation.

In the period elapse determination process, if within the valid periodof the initial check completed state and if the release switch 113 hasdetected the linking pin 112 at the release position, the safety brakefunction unit 22Fa causes a transition to the initial check completedstate and causes a transition of the display screen of the liquidcrystal monitor 32 to an autonomous drive start screen 32D illustratedin FIG. 22 to permit the transition of the drive mode from the manualdrive mode to the autonomous drive mode.

If an initial check is selected through an operation of a checkselection button 32 b on the safety brake check selection screen 32B inthe pre-condition establishment standby state, the safety brake functionunit 22Fa causes the display screen of the liquid crystal monitor 32 totransition to a safety brake check screen 32C illustrated in FIG. 17. Atthis time, an initial check button 32 c on the safety brake check screen32C is grayed out, as illustrated in FIG. 17, to indicate that theinitial check cannot be started through the operation of the initialcheck button 32 c.

In the pre-condition establishment standby state, if the release switch113 has detected the linking pin 112 at the release position, and if thebraking switch 114 has detected the linking pin 112 at the brakingposition, the safety brake function unit 22Fa determines that an errorhas occurred in one of the electric motor 102, the release switch 113,and the braking switch 114 and causes a transition to the errordetection state.

If the release switch 113 has not detected the linking pin 112 at therelease position in the pre-condition establishment standby state, thesafety brake function unit 22Fa causes a transition to the brake releasereturn operation state, and instructs the steering control unit 22C torelease the left and right brakes 42 by the operation of the electricmotor 102.

In the pre-condition establishment standby state, if the release switch113 has detected the linking pin 112 at the release position by theoperation of the electric motor 102 and if the first to ninth conditionsare all established while the braking switch 114 has not detected thelinking pin 112 at the braking position by the operation of the electricmotor 102, the safety brake function unit 22Fa causes a transition tothe initial check standby state and causes the display state of theinitial check button 32 c on the safety brake check screen 32C totransition to a normal display state illustrated in FIG. 18, to indicatethat the initial check can be selected through operation of the initialcheck button 32 c.

In the pre-condition establishment standby state, if the release switch113 has detected the linking pin 112 at the release position and none ofthe first to ninth conditions are established while the braking switch114 has not detected the linking pin 112 at the braking position, thesafety brake function unit 22Fa keeps the pre-condition establishmentstandby state and causes the display screen of the liquid crystalmonitor 32 to transition to the safety brake check screen 32Cillustrated in FIG. 17. At this time, an initial check button 32 c isgrayed out as illustrated in FIG. 17 on the safety brake check screen32C, to indicate that the initial check cannot be selected by theoperation of the initial check button 32 c.

In the initial check standby state, if the release switch 113 hasdetected the linking pin 112 at the release position and the brakingswitch 114 has detected the linking pin 112 at the braking position, inthe initial state, the safety brake function unit 22Fa determines thatan error has occurred in any of the electric motor 102, the releaseswitch 113, and the braking switch 114 and causes a transition to theerror detection state.

If the release switch 113 has not detected the linking pin 112 at therelease position in the initial check standby state, the safety brakefunction unit 22Fa causes a transition to the brake release returnoperation state and instructs the steering control unit 22C to releasethe left and right brakes 42 by the operation of the electric motor 102.

In the initial check standby state, if any of the first to ninthconditions is no longer established due to, for example, manualoperation of the left and right brake pedals 40 or the reverser leverwhile the release switch 113 has detected the linking pin 112 at therelease position, and the braking switch 114 has not detected thelinking pin 112 at the braking position, the safety brake function unit22Fa causes a transition to the pre-condition establishment standbystate and causes the display state of the initial check button 32 c onthe safety brake check screen 32C to transition to a grayout stateillustrated in FIG. 17, to indicate that the initial check cannot beselected through operation of the initial check button 32 c.

If the initial check button 32 c is operated in the initial checkstandby state, the safety brake function unit 22Fa causes a transitionto a braking operation check state, (“Check” in FIG. 24) and causes thesafety brake check screen 32C illustrated in FIG. 19 to indicate that aninitial check is in progress.

The safety brake function unit 22Fa instructs the steering control unit22C to brake the left and right brakes 42 by operating the electricmotor 102 in the braking operation check state. In this way, thesteering control unit 22C brakes the left and right brakes 42 by theoperation of the electric motor 102.

In the braking operation check state, if the release switch 113 hasdetected the linking pin 112 at the release position and the brakingswitch 114 has detected the linking pin 112 at the braking position, orif the braking switch 114 does not detect the linking pin 112 at thebraking position even after a predetermined braking operation checktime, the safety brake function unit 22Fa determines that an error hasoccurred in any one of the electric motor 102, the release switch 113,and the braking switch 114, and causes a transition to the errordetection state.

In the braking operation check state, if any one of the first to ninthconditions is no longer established due to, for example, manualoperation of the left and right brake pedals 40 or the reverser lever,the safety brake function unit 22Fa causes a transition to an initialcheck failure state (“Check_NG” in FIG. 24) and displays on the safetybrake check screen 32C that the initial check has failed, as illustratedin FIG. 20. When a predetermined display time elapses after thetransition to the initial check failure state, the safety brake functionunit 22Fa causes a transition to the initial state and causes thedisplay screen of the liquid crystal monitor 32 to transition to thesafety brake check selection screen 32B illustrated in FIG. 16. Then, ifthe check selection button 32 b on the safety brake check selectionscreen 32B illustrated in FIG. 16 is operated, the safety brake functionunit 22Fa causes a transition to the pre-condition establishment standbystate and causes the display screen of the liquid crystal monitor 32 totransition to the safety brake check screen 32C illustrated in FIG. 17.

In the braking operation check state, if the release switch 113 nolonger detects the linking pin 112 at the release position, and if theleft and right brake switches 25 have detected a shift of the left andright brake pedals 40 from the depression release position after thebraking switch 114 has detect the linking pin 112 at the brakingposition, and if the left and right brake sensors 26 have detected theleft and right brake pedals 40 at the maximum depression positions, thesafety brake function unit 22Fa determines that the left and right brakepedals 40 have been operated to the maximum depression positions, andthe left and right brakes 42 have switched to a braking state. Then, onthe basis of the determination, the safety brake function unit 22Facauses a transition to a release operation check standby state(“Check_Rev_Wait” in FIG. 24), and instructs the steering control unit22C to stop the braking operation of the left and right brakes 42 by theoperation of the electric motor 102. In this way, the steering controlunit 22C ends the braking operation of the left and right brakes 42 bythe operation of the electric motor 102.

In the release operation check standby state, if the release switch 113has detected the linking pin 112 at the release position, or if thebraking switch 114 has not detected the linking pin 112 at the brakingposition, the safety brake function unit 22Fa determines that an errorhas occurred in any one of the electric motor 102, the release switch113, and the braking switch 114, and causes a transition to the errordetection state.

If any one of the first to ninth conditions is no longer established,for example, as a result of manual operation of the left and right brakepedals 40 or the reverser lever, in the release operation check standbystate, the safety brake function unit 22Fa causes a transition to theinitial check failure state, and displays on the safety brake checkscreen 32C that the initial check has failed, as illustrated in FIG. 20.When a predetermined display time elapses after the transition to theinitial check failure state, the safety brake function unit 22Fa causesa transition to the initial state and causes the display screen of theliquid crystal monitor 32 to transition to the safety brake checkselection screen 32B illustrated in FIG. 16. Then, if the checkselection button 32 b on the safety brake check selection screen 32Billustrated in FIG. 16 is operated, the safety brake function unit 22Facauses a transition to the pre-condition establishment standby state andcauses the display screen of the liquid crystal monitor 32 to transitionto the safety brake check screen 32C illustrated in FIG. 17.

In the release operation check standby state, if the release switch 113no longer detects the linking pin 112 at the release position and thebraking switch 114 has detected the linking pin 112 at the brakingposition, or if the left and right brake switches 25 have detected ashift of the left and right brake pedals 40 from the depression releaseposition and a predetermined standby time has elapses after the left andright brake sensors 26 have detected the left and right brake pedals 40at the maximum depression positions, the safety brake function unit 22Facauses a transition to a release operation check state (“Check_Rev inFIG. 24).

The safety brake function unit 22Fa instructs the steering control unit22C to release the left and right brakes 42 by operating the electricmotor 102 in the release operation check state. In this way, thesteering control unit 22C releases the left and right brakes 42 by theoperation of the electric motor 102.

In the release operation check state, if the release switch 113 hasdetected the linking pin 112 at the release position and the brakingswitch 114 has detected the linking pin 112 at the braking position, orif the release switch 113 has not detected the linking pin 112 at therelease position even after a predetermined release operation checktime, the safety brake function unit 22Fa determines that an error hasoccurred in any one of the electric motor 102, the release switch 113,and the braking switch 114, and causes a transition to the errordetection state.

In the release operation check state, if any of the first to ninthconditions is no longer established, for example, due to manualoperation of the left and right brake pedals 40 or the reverser lever,the safety brake function unit 22Fa causes a transition to the initialcheck failure state and displays on the safety brake check screen 32Cthat the initial check has failed, as illustrated in FIG. 20. When apredetermined display time elapses after the transition to the initialcheck failure state, the safety brake function unit 22Fa causes atransition from the initial check failure state to the initial state andcauses the display screen of the liquid crystal monitor 32 to transitionto the safety brake check selection screen 32B illustrated in FIG. 16.Then, if the check selection button 32 b on the safety brake checkselection screen 32B illustrated in FIG. 16 is operated, the safetybrake function unit 22Fa causes a transition to the pre-conditionestablishment standby state and causes the display screen of the liquidcrystal monitor 32 to transition to the safety brake check screen 32Cillustrated in FIG. 17.

In the release operation check state, if the release switch 113 hasdetected the linking pin 112 at the release position, and the left andright brake switches 25 and the left and right brake sensors 26 havedetected the left and right brake pedals 40 at the depression releaseposition while the braking switch 114 has not detected the linking pin112 at the braking position, the safety brake function unit 22Fadetermines that the left and right brake pedals 40 have been operated tothe depression release position, and the left and right brakes 42 haveswitched to the released state. Then, on the basis of the determination,the steering control unit 22C is instructed to stop the releaseoperation of the left and right brakes 42 by the operation of theelectric motor 102. In this way, the steering control unit 22C ends thebraking operation of the left and right brakes 42 by the operation ofthe electric motor 102. The safety brake function unit 22Fa then causesa transition to an initial check successful state (“Check_Comp” in FIG.24) and displays on the safety brake check screen 32C that the initialcheck has been completed, as illustrated in FIG. 21.

The safety brake function unit 22Fa keeps the display of the completionof the initial check on the safety brake check screen 32C for apredetermined time in the initial check successful state. When thepredetermined time elapses, the safety brake function unit 22Fa causes atransition to an initial check completed state (operation confirmedstate) (“Check_OK” in FIG. 24), causes the display screen of the liquidcrystal monitor 32 to transition to the autonomous drive start screen32D illustrated in FIG. 22, and permits the transition of the drive modefrom the manual drive mode to the autonomous drive mode.

When various setting operations necessary for the autonomous drive ofthe tractor 1, such as the setting of the engine speed for autonomousdrive through an operation of the accelerator bar and the setting of thevehicle speed for autonomous drive through an operation of the speedchange lever, are performed after the safety brake function unit 22Fahas caused a transition to the initial check completed state, allconditions for the transition of the drive mode to the autonomous drivemode are established. In a state in which all conditions areestablished, if an autonomous drive start button 32 d displayed on theautonomous drive start screen 32D illustrated in FIG. 22 is operated,the autonomous drive control unit 22F causes the drive mode of thetractor 1 to transition from the manual drive mode to the autonomousdrive mode, notifies the mobile communication terminal 3 about thetransition of the drive mode of the tractor 1 to the autonomous drivemode, and enables the autonomous drive to be started by an operation ofthe mobile communication terminal 3.

In other words, when the tractor 1 is autonomously driven after thedrive mode has transitioned to the autonomous drive mode, the left andright brakes 42 are preliminarily confirmed to operate normally assafety brakes through confirmation of the operation in advance. In thisway, in case any of the above-described errors occurs inside the vehiclein the autonomous drive mode, the left and right brakes 42 can beoperated normally as safety brakes, and the tractor 1 can be certainlybraked and stopped.

As it is apparent from the description above, the initial check(operation confirmation process) includes a first operation confirmationprocess and a second operation confirmation process. The first operationconfirmation process confirms whether or not the electric motor 102 isoperating normally on the basis of the detection information from therelease switch (first operation sensor) 113 and the braking switch(first operation sensor) 114 that detect the operation of the electricmotor 102. The second operation confirmation process confirms whether ornot the left and right brakes 42 are operating normally on the basis ofthe detection information from the left and right brake switches (secondoperation sensor) 25 and the left and right brake sensors (secondoperation sensor) 26 that detect the operation of the left and rightbrakes 42.

In this way, the operation of the electric motor 102 that causes theleft and right brakes 42 to operate as the safety brakes and theoperation of the left and right brakes 42 functioning as safety brakesare confirmed separately in the initial check (operation confirmationprocess) for checking whether or not the left and right brakes 42operate normally as safety brakes. As a result, the initial check can beperformed with high accuracy, and the reliability of the initial checkcan be enhanced.

When an initial check is to be performed, the safety brake function unit22Fa first performs the pre-condition determination process, and startsthe initial check when all conditions for starting the initial check,which are necessary for starting the initial check, are established, asdescribed above. In this way, it possible to avoid inconveniences, suchas a decrease in the reliability of the initial check caused by adecrease in the load applied to the electric motor 102 during theinitial check due to the left and right brake pedals 40 being depressedor the left and right brake pedals 40 being decoupled, or theincompletion of the initial check due to errors in the speed changecontrol unit 22B, the CAN communication, etc.

As described above, the valid period is set for the initial checkcompleted state. Therefore, the safety brake function unit 22Fa performsthe period elapse determination process described above in the initialcheck completed state. If the valid period elapses in the period elapsedetermination process, the safety brake function unit 22Fa causes atransition from the initial check completed state to the initial state,as illustrated in FIG. 24.

At this time, if the drive mode is the autonomous drive mode, the safetybrake function unit 22Fa causes the drive mode to transition from theautonomous drive mode to the manual drive mode, and prohibits atransition to the autonomous drive mode. The safety brake function unit22Fa causes the display screen of the liquid crystal monitor 32 totransition to the safety brake check selection screen 32B illustrated inFIG. 16. If the check selection button 32 b on the safety brake checkselection screen 32B illustrated in FIG. 16 is operated, the safetybrake function unit 22Fa performs the initial check with theabove-described state transition, and causes the display screen of theliquid crystal monitor 32 to transition to the autonomous drive startscreen 32D illustrated in FIG. 22 after a transition to the initialcheck completed state and permits the transition of the drive mode fromthe manual drive mode to the autonomous drive mode.

In this way, an initial check is performed regularly, for example, whenthe tractor 1 is autonomously driven for several days. For this reason,it is possible to effectively suppress the risk of the left and rightbrakes 42 not operating normally as safety brakes in case any of theerrors described above or any other errors occur inside the vehicle.

Note that, when the valid period of the initial check completed stateelapses in the period elapse determination process, and the drive modeis already set to the autonomous drive mode, the safety brake functionunit 22Fa may enable the initial check completed state while the userkeeps the autonomous drive mode, and disable the initial check completedstate when the user ends the autonomous drive mode, to cause atransition from the initial check completed state to the initial state.

On the other hand, when the drive mode is the manual drive mode, thesafety brake function unit 22Fa indicates that the valid period of theinitial check completed state has elapsed, on the display screen of theliquid crystal monitor 32 or the like.

In this way, when the tractor 1 is manually driven by the passenger, itis possible to inform the passenger in advance that an initial check isrequired for the transition of the drive mode to the autonomous drivemode. It is also possible to prevent a decrease in work efficiency dueto periodical initial checks being performed during manual drive inwhich the left and right brakes 42 are not operated as safety brakes.

If any of the errors described above occur inside the vehicle in theinitial check completed state, the safety brake function unit 22Facauses a transition to the safety brake operation state (“Brake_Move” inFIG. 24), and instructs the steering control unit 22C to brake the leftand right brakes 42 by the operation the electric motor 102. In thisway, the steering control unit 22C brakes the left and right brakes 42by the operation of the electric motor 102.

In the initial check completed state, if the release switch 113 hasdetected the linking pin 112 at the release position, and the brakingswitch 114 has detected the linking pin 112 at the braking position, thesafety brake function unit 22Fa determines that an error has occurred inone of the electric motor 102, the release switch 113, and the brakingswitch 114, and causes a transition to the error detection state.

In the initial check completed state, if within the valid period of theinitial check completed state, and the release switch 113 has notdetected the linking pin 112 at the release position while no error hasoccurred inside the vehicle, the safety brake function unit 22Fa causesa transition to the checked brake release return operation state(“OK_Rev” in FIG. 24), and instructs the steering control unit 22C torelease the left and right brakes 42 by the operation of the electricmotor 102. In this way, the steering control unit 22C releases the leftand right brakes 42 by the operation of the electric motor 102.

In the checked brake release return operation state, if the releaseswitch 113 has not detected the linking pin 112 at the release positioneven after a predetermined time for releasing the braking has elapsed,the safety brake function unit 22Fa determines that an error hasoccurred in any of the electric motor 102, the release switch 113, andthe braking switch 114 and causes a transition to the error detectionstate.

In the checked brake release return operation state, if the releaseswitch 113 has detected the linking pin 112 at the release positionwithin the predetermined time for releasing the braking, the safetybrake function unit 22Fa causes a transition to the initial checkcompleted state (“Check_OK” in FIG. 24), causes the display screen ofthe liquid crystal monitor 32 to transition to the autonomous drivestart screen 32D illustrated in FIG. 22, and permits a transition of thedrive mode from the manual drive mode to the autonomous drive mode.

In the brake release return operation state (“Rev_Start” in FIG. 24), ifthe release switch 113 has detected the linking pin 112 at the releaseposition and the braking switch 114 has detected the linking pin 112 atthe braking position, or if the release switch 113 has not detected thelinking pin 112 at the release position even after the predeterminedtime for releasing the braking has elapsed, the safety brake functionunit 22Fa determines that an error has occurred in any one of theelectric motor 102, the release switch 113, and the braking switch 114,and causes a transition to the error detection state.

In the brake release return operation state, if the release switch 113has detected the linking pin 112 at the release position, and if thebraking switch 114 has not detected the linking pin 112 at the brakingposition, the safety brake function unit 22Fa causes a transition to theinitial state (“Start” in FIG. 24).

In the safety brake operation state (“Brake_Move” in FIG. 24), if therelease switch 113 detects the linking pin 112 at the release positioneven after a predetermined time for brake operation has elapsed, or ifthe braking switch 114 has not detected the linking pin 112 at thebraking position, the safety brake function unit 22Fa determines that anerror has occurred in any one of the electric motor 102, the releaseswitch 113, and the braking switch 114, and causes a transition to theerror detection state.

In the safety brake operation state, if the release switch 113 no longerdetect the linking pin 112 at the release position, and if thepredetermined time for brake operation has elapsed while the brakingswitch 114 has detected the linking pin 112 at the braking position, thesafety brake function unit 22Fa determines that the left and right brakepedals 40 have been operated to the maximum depression position and theleft and right brakes 42 have switched to a braking state. Then, on thebasis of the determination, the safety brake function unit 22Fa causes atransition to a safety brake operation hold state (“Brake_Stop” in FIG.24), and instructs the steering control unit 22C to stop the brakingoperation of the left and right brakes 42 by the operation of theelectric motor 102. In this way, the steering control unit 22C ends thebraking operation of the left and right brakes 42 by the operation ofthe electric motor 102. As a result, the left and right brakes 42 can beheld in an operated state as safety brakes, and the tractor 1 can bekept in the braking stop state.

As illustrated in FIG. 25, in the error detection state, the safetybrake function unit 22Fa causes a transition to an electric motor errorstate (“Err_Actuator” in FIG. 25), an ON detection error state (ErrPosition_ON in FIG. 25), or an OFF detection error state(“Err_Position_Off” in FIG. 25) in accordance with the detection statesof the release switch 113 and the braking switch 114. In any of theerror states, if the transition is not from the safety brake operationstate, the state transitions to a brake released state for error(“Err_Rev” in FIG. 25), and the steering control unit 22C is instructedto release the left and right brakes 42 by the operation of the electricmotor 102. In this way, the steering control unit 22C releases the leftand right brakes 42 by the operation of the electric motor 102. Then,the left and right brakes 42 can be returned to the released state bythe release operation, and the tractor 1 can be manually driven by thepassenger.

If a predetermined time for a release operation elapses in the brakereleased state for error, the safety brake function unit 22Fa causes atransition to an error state (“Err_Actuator” in FIG. 25) and keeps thisstate.

In any one of the electric motor error state, the ON detection errorstate, and the OFF detection error state, the safety brake function unit22Fa causes a transition to the error state (“Err Actuator” in FIG. 25)if the transition is from the safety brake operation state, and keepsthis state. In this way, the left and right brakes 42 can be kept in anoperated state as safety brake in the above-stated error state, and thetractor 1 can be kept in a braking stop state.

OTHER EMBODIMENTS

Other embodiments of the present invention will now be described.

The configurations of the respective embodiments described below are notnecessarily applied independently, but may be applied under combinationwith the configurations of the other embodiments.

(1) Another typical embodiment regarding the configuration of the workvehicle is as follows.

For example, the work vehicle may be configured in a semi-crawlerspecification with left and right crawlers as driving devices 10 and 11in place of the left and right front wheels 10 and the left and rightrear wheels 11.

For example, the work vehicle may be configured in a full-crawlerspecification with left and right crawlers as driving devices 10 and 11in place of the left and right front wheels 10 and the left and rightrear wheels 11.

For example, the work vehicle may be configured in an electricspecification with an electric motor in place of the engine 14.

For example, the work vehicle may be configured in a hybridspecification with the engine 14 and an electric motor.

For example, the work vehicle may be configured with a protective frameextending above tractor 1, in place of the cabin 13.

(2) Another typical embodiment regarding the configuration of theelectric actuator 102 is as follows.

For example, the electric actuator 102 may be left and right electricmotors 102 that individually operate the left and right brake pedals 40.

For example, the electric actuator 102 may be a single electric cylinderthat operates the left and right brake pedals 40 coupled by the couplingmechanism 55.

For example, the electric actuator 102 may be left and right electriccylinders that individually operate the left and right brake pedals 40.

(3) The foot brake 42 may be a single foot brake operated by a singlebrake pedal provided in the driver unit 12.

(4) The operation tool 84 for brake release may be, for example, anoperation button displayed on the liquid crystal monitor 32.

INDUSTRIAL APPLICABILITY

The present invention may be applied to a work vehicle, such as atractor, a riding mower, a riding rice transplanter, a combine, acarrier, a wheel loader, or a snowplow.

DESCRIPTION OF REFERENCE NUMERALS

-   -   2 autonomous drive unit    -   3 wireless communication device (mobile communication terminal)    -   10 driving device (front wheel)    -   11 driving device (rear wheel)    -   12 driver unit    -   14 engine    -   22Fa control unit (safety brake function unit)    -   23 vehicle condition detection device    -   32 a mode selector (mode selection button)    -   42 foot brake (brake)    -   84 operation tool (key switch)    -   90 wireless communication device (emergency stop remote control)    -   102 electric actuator (electric motor)

1: A work vehicle comprising: a boarding-type driver unit; a foot brakethat brakes a driving device; an autonomous drive unit that enablesautonomous drive of a vehicle; and an electric actuator that switchesthe foot brake between a braking state for braking the driving deviceand a released state for releasing the braking, wherein, the driver unitincludes a mode selector that enables selection of an autonomous drivemode in which the autonomous drive unit autonomously drives the vehicle,the autonomous drive unit includes a control unit that controls anoperation of the electric actuator, and in the autonomous drive mode, ifan error is detected inside the vehicle based on detection informationfrom a vehicle state detection device that detects a state of eachcomponent in the vehicle, or if an emergency stop command is obtainedfrom a wireless communication device that is capable of wirelesscommunication with the autonomous drive unit, the control unit controlsthe operation of the electric actuator and switches the foot brake fromthe released state to the braking state. 2: The work vehicle accordingto claim 1, wherein, the driver unit includes an operating tool forbrake release, and if the operation tool is manually operated in thebraking state of the foot brake by the operation of the electricactuator, the control unit controls the operation of the electricactuator and switches the foot brake from the braking state to thereleased state. 3: The work vehicle according to claim 1, wherein if theautonomous drive mode is deselected when the foot brake is to beswitched to the braking state and if the autonomous drive mode isselected by the mode selector after the deselection, the control unitdetermines whether or not an error has occurred inside the vehicle onthe basis of detection information from the vehicle state detectiondevice and permits a transition to the autonomous drive mode when it isdetermined that no errors have occurred inside the vehicle. 4: The workvehicle according to claim 1, comprising: an electronically controlledengine, wherein if the control unit controls the operation of theelectric actuator and the foot brake is switched from the released stateto the braking state, the control unit automatically stops the engine.5: The work vehicle according to claim 4, wherein if the operation ofthe electric actuator switches the foot brake to the braking state, andif power is turned on again by turning on a key switch provided in thedriver unit after the power has been turned off by turning off the keyswitch in a state in which the engine is automatically stopped, thecontrol unit permits activation of the engine and switches the footbrake form the braking state to the released state by controlling theoperation of the actuator.